It is conventionally known that chemical prepared toners are produced by a polymerization method or an emulsification dispersion method. Among these methods, when the toner is produced by the emulsification dispersion method, a mixture containing, for example, a resin binder and a colorant is mixed and emulsified in an aqueous medium to obtain toner particles. In this method, for example, upon preparing a polyester emulsion using a polyester as the resin binder, there has been generally used a phase inversion emulsification method using an organic solvent or a forced emulsification method conducted under a high-pressure/high-temperature condition. However, the former method is burdensome for removal and recovery of the organic solvent and waste water treatment, whereas the latter method requires the use of a special apparatus.
As conventional techniques using no organic solvent, there is disclosed, for example, the process for producing a toner for developing an electrostatic latent image which includes the steps of (1) mixing a molten colored resin obtained by heat-melting a kneaded material composed of an ionic group-containing synthetic resin for a toner for developing an electrostatic latent image and a coloring pigment, with an aqueous medium containing a substance capable of neutralizing the ionic group which medium is heated to a temperature not lower than a softening point of the synthetic resin by heating it under pressure; (2) while maintaining the resulting mixture at the temperature not lower than a softening point of the synthetic resin, finely dispersing the molten colored resin in the aqueous medium by a mechanical means; (3) immediately after dispersing, rapidly cooling the obtained dispersion to produce a water dispersion of fine colored resin particles; (4) separating the fine colored resin particles from the dispersion; and (5) drying the thus separated fine colored resin particles (refer to JP 9-311502A).
Further, there is disclosed the process for producing a toner for developing an electrostatic latent image which includes the steps of heat-melting a raw toner material containing at least a polyester resin to produce a melt of the raw toner material; emulsifying the obtained melt in an aqueous medium to form fine resin particles; and then aggregating and further fusing the fine resin particles to produce an associated product of the fine resin particles (refer to JP 2002-351140A).
However, in any of the conventional techniques disclosed in these patent documents, the resin is heated to a temperature not lower than a softening point thereof to form a melt, and the obtained melt is emulsified and dispersed using a special apparatus such as a high-speed rotating continuous type emulsifying and dispersing device.